Breast cancer patients with even the tiniest spread of the disease to a lymph node have a much higher risk of it recurring years later and may need more treatment than just surgery, new research suggests.

For years, doctors and patients have struggled with what to do about a microscopic tumor or stray cancer cells in a lymph node. Women with “micro tumors” usually are given estrogen-blocking drugs, chemotherapy or both; those with isolated cancer cells usually are not, because those were thought to be of low concern.

The new study challenges that view. It suggests that either type of metastasis, or spread, raises a woman’s risk of having cancer show up in the breast or anywhere else in the next five years by about 50 percent.

“This took an area that was very gray and I think made it black and white,” said Dr. Linda Vahdat, director of breast cancer research at Weill Cornell Medical College and an adviser for the breast cancer patient Web site of ASCO, the American Society of Clinical Oncology.

“I think it will influence treatment,” she said of the study. “If we’re considering treating the patient, we probably should.”

Dr. Daniel Hayes, director of breast cancer treatment at the University of Michigan, agreed.

“It really does look like our biases are wrong,” he said. “For the first time, it suggests that isolated tumor cells or micrometastases do have biological significance.”